The present invention relates generally to semiconductor processing and, in particular, to methods for the determination of film continuity and growth modes in thin dielectric films.
Thickness scaling of deposited high-k gate dielectrics is limited by physiochemical properties of the deposition process and is a function of numerous factors such as surface energies, steric hindrance, surface diffusion, grain growth and coalescence. The ability to measure the transition point between a film suffering from discontinuities, which limits the effective leakage reduction and capacitance gain in gate dielectrics to a continuous film, is important in developing advanced high performance gate dielectric films for 45 nm devices and beyond.
A well-known problem with high-k gate dielectrics is the inability to scale the film thickness below ˜25 Å. For example, hafnium oxide (HfO2) nucleates in islands on interfacial silicon oxynitride (SiON) layers that do not coalesce into a continuous film until ˜25 Å. This phenomenon causes increased leakage currents in film with a thickness below ˜25 Å and prevents gate dielectric scaling below this value. This in turn prevents scaling of thickness-in-inversion (Tinv) to values required by the gate roadmap for future integrated circuit chips.
Different interfaces and growth conditions strongly influence the growth mode and coalescent point of thin films that nucleate in islands. To this extent, the evaluation of the effects of surface preparation (e.g., precleaning solution, substrate temperature, interfacial barrier material, precursor chemistry, etc.) on the nucleation and growth of dielectric materials is important for the determination of optimum conditions for layer-by-layer growth. In the past, this type of analysis was performed using expensive, destructive, and time-consuming analytical chemical techniques that required a skilled operator and extensive sample preparation. Examples of such techniques include Rutherford Backscattering Spectroscopy (RBS), Medium Energy Ion Scattering (MEIS), and High-Resolution Transmission Electron Microscopy (HRTEM). Unfortunately, these types of chemical and physical techniques have been found to provide erroneous results regarding film continuity for ultra-thin films. Accordingly, there is a need for a method for evaluating the effects of surface preparation on the nucleation and growth of dielectric materials that obviates these and other problems associated with the prior art.